Mobile display devices such as cellphones and tablet PCs are apt to be damaged when hit or scratched, for example. In order to prevent such damage, the users often manually apply a protective film to the surface of their mobile display device on their own. When the users apply a film to a product on their own, they usually apply a film in a general environment, not in a controlled environment such as a clean room environment or vacuum. In a general environment, however, it is difficult to manually apply a film while sufficiently preventing entry of foreign substances and air bubbles between the product and the film. Also in cases where a film is applied to a large surface such as windows at construction sites or display windows of convenience stores or department stores, the application cannot be conducted in an environment where foreign substances are controlled, such as a clean room environment. It is therefore also difficult to apply a film while preventing entry of foreign substances between such a surface and the film as in the case of application to mobile display devices.
There is a film application method that can be manually performed and prevent entry of foreign substances and air bubbles even in a general environment. The method includes controlling the application position of the film and removing air bubbles using soapy water, and drying the film in the air. This method has advantages such as a fine control of the application position, and is used by professionals of film application when they apply to a glass window a film on which a company logo or an advertisement is printed. However, this method is inconvenient for general users because soapy water is required and air-drying takes time, for example. Also, the method can still be improved from the viewpoint of preventing entry of foreign substances, though the method can sufficiently remove air bubbles.
Meanwhile, mainly for cases of applying a film to a product in a factory, there are various known treatment methods and devices for preventing entry of foreign substances and air bubbles between the film and the product. Common methods here include, for example, application methods performed in a clean room or in vacuum (e.g. Patent Literature 1). For example, for application of a film to a liquid crystal panel, a large-scale cleaning system is used.
Patent Literature 2 discloses a method including supplying a liquid whose temperature is higher than the room temperature to remove foreign substances, dirt and grime on the surface of the liquid crystal panel. Patent Literature 3 discloses an application apparatus configured to automatically clean the surface of the main unit of the liquid crystal panel with its foreign-substance-cleaning roller before applying a polarizer to the surface.
Other known methods are those removing foreign substances by making the foreign substances stick to an adhesive layer. Patent Literature 4 discloses a foreign-substance-removing adhesive tape whose adhesive layer surface picks up foreign substances on the surface of a product such as a semiconductor wafer or a glass substrate to remove the foreign substances. Patent Literature 5 discloses a foreign-substance-removing sheet designed to be applied to a conveyer member when used, wherein the separator for protection of the surface of the foreign-substance-removing layer is applied to the foreign-substance-removing layer by an adhesive layer.